PROJECT SUMMARY Epithelial Ovarian Cancer (EOC) is the 5th leading cause of cancer death in women. EOC has a 90% survival rate if detected early, but due to its non-specific symptoms, many cases go undetected until metastases are already present. In its late metastatic stages, there are no effective treatments available for EOC. Furthermore, EOC recurrence is common, and is frequently associated with loss of sensitivity to available therapies. Thus, there is a dire need for novel EOC therapeutics, especially those that target metastasis. One way that tumor cells can migrate to new sites is via chemokines. Chemokines are small secreted proteins that direct the cell migration, or chemotaxis, in both disease and homeostatic processes. Chemokines trigger cell migration by binding to their cognate cell-surface receptors, which are members of the G-Protein Coupled Receptor superfamily. Binding of chemokines to their receptors triggers a signaling cascade, culminating in cytoskeletal reorganization and chemotaxis to areas of high chemokine concentration. Tumor cells can hijack this process by upregulating chemokine and chemokine receptor expression, allowing tumor cells to migrate to distant sites along chemokine gradients. The chemokine receptor XCR1 has increased expression in many cancers and has been associated with increased tumor cell proliferation and migration. Silencing of XCR1 in murine models has been shown to significantly decrease metastasis of EOC. Our lab recently performed in-depth characterization of XCL1, the chemokine ligand for XCR1, leading to the identification of ligand residues that are critical for receptor binding and activation. This proposal aims to advance this knowledge by elucidating important residues in XCR1, which is a more viable drug target than its ligand, and to study the functional role of the XCL1-XCR1 axis in the metastasis of epithelial ovarian cancer. Specifically, the goal of this fellowship is use complementary biochemical and functional approaches to test the hypothesis that specific intermolecular contacts at the XCL1-XCR1 interface are critical drivers of EOC cell migration. The fellowship research will consist of two specific aims. Aim 1 will test the hypothesis that certain residues in XCR1's orthosteric binding pocket are crucial for XCR1-XCL1 signaling. Aim 2 will test the hypothesis that XCR1 is expressed by human EOC cell lines not previously probed for XCR1 expression, and that variant XCL1 proteins will elicit unique chemotactic profiles in XCR1-positive human EOC cells including those discovered in the first part of this aim. The research will take place in the Brian Volkman lab at the Medical College of Wisconsin, a highly collaborative and stimulating environment that is well equipped with the infrastructure and equipment to make this proposal a success. In all, understanding the fundamental structural characteristics of chemokine ligand-receptor interactions will reveal mechanisms driving tumor progression and metastasis. Exploiting the complementary relationship of structure and function will yield vital insight towards the development of better and more specific therapeutics targeting cancer progression and metastasis.